FIG. 1 is a schematic sectional view of a conventional LED structure. The LED structure 124 includes a substrate 100, a buffer layer 102, an n-type semiconductor layer 104, an active layer (light emitting layer) 106, a p-type semiconductor layer 108, a p-type ohmic contact layer 112, a reflective layer 114, an n-type ohmic contact layer 116, an n-type electrode 118, a p-type electrode 120 and a passivation layer 122.
In the LED structure 124, the buffer layer 102 is disposed on the substrate 100. The n-type semiconductor layer 104 is disposed on the buffer layer 102. The active layer 106 is disposed on a part of the n-type semiconductor layer 104, so that the n-type semiconductor layer 104 has an exposed part 110. The p-type semiconductor layer 108 is disposed on the active layer 106. The p-type ohmic contact layer 112 and the reflective layer 114 are stacked in sequence on the p-type semiconductor layer 108. The p-type electrode 120 is disposed on a part of the reflective layer 114. Furthermore, the n-type ohmic contact layer 116 and the n-type electrode 118 are stacked in sequence on the exposed part 110 of the n-type semiconductor layer 104. The passivation layer 122 covers the p-type electrode 120, the reflective layer 114, the p-type ohmic contact layer 112, the p-type semiconductor layer 108, the active layer 106, the n-type semiconductor layer 104, the n-type ohmic contact layer 116 and the n-type electrode 118, and exposes a part of the p-type electrode 120 and a part of the n-type electrode 118.
In the conventional LED structure 124, the p-type ohmic contact layer 112 together with the reflective layer 114 directly contact the p-type semiconductor layer 108. When the LED structure 124 is operating under a large current for a long time, the heat generated by the active layer 106 easily deteriorates the reflective layer 114, and thus not only the power of the device is attenuated but also the luminous efficiency of the device may be influenced.
Furthermore, the flip-chip process requires the n-type electrode 118 and the p-type electrode 120 to have a large area. However, the n-type electrode 118 of the conventional LED structure 124 is directly disposed on the n-type ohmic contact layer 116, so when the n-type semiconductor layer 104 is defined, a larger area needs to be removed to enable the exposed part 110 of the n-type semiconductor layer 104 to have a large area, for disposing the n-type ohmic contact layer 116 and the n-type electrode 118 having the large area. Yet, as shown in FIG. 1, the increase of the area of the n-type ohmic contact layer 116 and the n-type electrode 118 will relatively reduce the light-emitting area of the active layer 108, thus reducing the luminous efficiency of the LED structure 124.